The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 (Severinsky).
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels. A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and an electric motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a parallel/series “split” configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier gear. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or driveability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shut down. Nevertheless, new ways must be developed to optimize the HEV's potential benefits.
One such area of HEV development is torque control of the engine, which requires an accurate estimate of engine torque.
HEV systems to control or determine engine torque or motor torque are generally known in the art. For example, Tabata et al., U.S. Pat. No. 5,951,614, teaches an apparatus for controlling an HEV drive system having a transmission disposed between a vehicle drive wheel and an assembly of an engine and a motor/generator, the apparatus including a torque reduction control device for reducing the input torque of the transmission during a shifting action of the transmission.
Bader, U.S. Pat. No. 6,307,276, teaches a method for operating a parallel hybrid electric vehicle, with an internal combustion engine which is connected to a drive shaft via a clutch and a manual transmission, and with a three-phase machine (a traction motor) which is directly coupled with its rotor to a countershaft of the manual transmission and is connected to an electrical energy store (a battery) via a three-phase converter. A time average of the driving torque required during a respective predeterminable travel time interval is determined by a hybrid drive control unit. The power outputs of the internal combustion engine and of the three-phase machine are controlled so that the internal combustion engine outputs driving torque corresponding to the time average determined, and the three-phase machine outputs the difference between the driving torque currently required and the driving torque delivered by the internal combustion engine.
Deguchi et al., U.S. Pat. No. 6,233,508, teaches a system where a target drive torque is calculated based on a detected value for vehicle speed and a detected value for an accelerator pedal depression amount. A generator torque is calculated for a motor based on a battery state of charge (SOC). An engine is controlled to a torque value that achieves a target drive torque and a generator torque as a target engine torque. The motor is controlled to a value that is the difference of a target drive torque and an engine torque estimation value as a target motor torque.
Tabata et al., U.S. Pat. No. 6,081,042, teaches a hybrid drive system for a motor vehicle, wherein a controllable device such as an automatic transmission or a center differential device is disposed between drive wheels of the vehicle and a drive power source consisting of an engine operated by combustion of a fuel, and an electric motor operated with an electric energy, and the engine and/or the electric motor is/are operated for driving the motor vehicle in different running modes. The controllable device is controlled by a control device on the basis of an input torque received by the controllable device. The control device is adapted to estimate the input torque of the controllable device depending upon a currently selected one of the running modes, or effect learning control of the controllable device in different manners corresponding to the different running modes.
The prior art has met the general needs of controlling an HEV's engine. Nevertheless, to fully achieve the goals of an HEV's performance, drivability, and efficiency, a more accurate system for controlling engine torque is needed.